A large number of plastic bottles and similar plastic containers that are now used can be produced in a stretch-blow-molding process. In this method, a so-called preform of an elongated, tube-like shape, which can have a base on one longitudinal end and a neck section with formed threaded sections or the like on the other longitudinal end, is inserted into a mold cavity of a blow mold and blown in through a medium that is injected with overpressure. In this case, the preform is additionally elongated in the axial direction with an elongated mandrel that is run in through the neck opening. After the elongation/blow-molding process, the finished plastic container is demolded from the blow mold.
The preform can be produced in a separate injection-molding method before the stretch-blow-molding process. The preforms can also be produced in an impact-extruding method or else by extrusion blow-molding process. In the so-called single-stage stretch-blow-molding process, the preform can be reshaped immediately after its production to form a plastic container with no cooling or storage in between. In most cases, however, the plastic containers can be produced in a two-stage method, in which in a separate method, first the preforms are produced, cooled, and intermediately stored for later use. The production of the plastic containers can be carried out in a manner separated in space and time in a separate stretch-blow-molding process. In this later stretch-blow-molding process, the preforms can be heated again in order to produce plastic bottles therefrom. For example, using infrared radiation, a desired temperature profile, which can be used for the stretch-blow-molding process, can be set via the axial and/or radial extension of the preform. After the preform is inserted into the mold tool, the latter can be radially formed by means of a gas that can be injected with overpressure, and in this case stretched in axial direction with a bar. Then, the finished plastic container can be demolded.
A large number of the known preforms have a support ring, which can separate the elongated preform body from the neck section. The support ring can be used to transport the preform and the plastic container produced therefrom. In the stretch-blow-molding device, the preform can be supported via the support ring on the mold tool, so that only the preform body projects into the mold cavity. The neck section can no longer be changed during the stretch-blow-molding process. A so-called snap ring, which can serve as a counter bearing for a safety cap on the finished stretch-blow-molded plastic container, can be formed between the support ring and the threaded sections made on the neck section. Such safety caps are known, for example, from beverage bottles. When unscrewing the safety cap, an annular section of the safety cap, for which the snap ring forms a counter bearing, at least partially separates from the other cap. As a result, it is indicated to the consumer, even in the case of a reclosed bottle, that the bottle has already been opened once.
In the production of mass-produced articles, such as, for example, plastic bottles made of polyethylene terephthalate (PET), the amount of material used represents a decisive factor for competitiveness and ecological balance. Because of the very high number of pieces, in which plastic bottles can be produced, reductions in material weight in the decigram range can very quickly lead to a savings in material in the ton range. Therefore, major efforts were undertaken in the past to decrease the material weight of the preforms for plastic bottles, for example, PET bottles. With the known preforms, the optimum material weight was believed to have been reached, and the plastic bottles produced from the preforms had reached the necessary mechanical strengths and temperature stabilities. In the previous efforts to reduce the material weight, multiple modifications of the stretch-blow-molding plants and the bottling plants were necessary. However, this can be unsatisfactory state both from the standpoint of the operator of stretch-blow-molding plants and from the standpoint of the filler of plastic containers produced from the preforms.
In WO 2006/027092 A1, for example, a preform for a wide-mouth container, which can have a neck section that is greatly widened in diameter relative to the preform body, is described. In the case of this preform, a support ring can be eliminated. The support of the preform relative to the mold tool can be done via a circumferential annular collar at the transition from the preform body to the widened neck section. For the transport of the preform and the plastic container produced from the preform, specially designed grippers, whose gripping surface can be matched to the peripheral contour of the neck section projecting from the mold tool, can be necessary. Specifically, the preform can have a savings of material by eliminating the support ring. In addition, the preform can be designed for the production of wide-mouth containers, however, for the transport of the preform and the plastic container produced from the preform, specifically designed grippers can be used. The grippers should engage in a threaded structure that can be arbitrarily aligned, without colliding with the threading. In addition, the preform picked up by the grippers should not be changed with respect to the orientation of its longitudinal axis in order to avoid an inclined position of the preform. With respect to the fact that the grippers engage two areas of the neck area that are opposite to one another and can very easily set a tilting moment depending on the axial position of the contact point, it is immediately clear that grippers that are suitable for the known preform can have a relatively complex structure and therefore greatly increase the overall cost of the equipment.
After their production, preforms can be decanted randomly in large containers, such as, for example, cartons, bags, mesh crates, octabins, etc., and transported. For further processing in the stretch-blow-molding method, the preforms can be filled from the containers into a hopper upstream from a stretch-blow-molding device and separated. The preforms pass through the hopper onto an ascending conveyor, by means of which they are transported intermittently or continuously in small quantities to a roll sorter. In the roll sorter, the preforms can be oriented corresponding to their center of gravity, in such a way that they can be suspended in a slot, with the preform body pointing downward and can slip individually against the stretch-blow-molding device. The preforms can be held via the support ring or a comparable radial projection between the neck section and the perform body in the roll sorter. If the center of gravity of the preform clearly lies below the support ring or the radial projection in the area of the preform body, the preforms can be correctly aligned and leave the roll sorter with the preform body pointing downward. In order therefore to achieve a correct alignment of the preforms, the known preforms can be in many cases designed with a comparatively long preform body. However, with stretch-blow-molding, this can result in a length-stretch ratio, which can have a negative effect on the strength of the stretch-blow-molded plastic container. In order to impart the necessary strength to the stretch-blow-molded plastic container, in contrast, the desire therefore exists for preforms that have a shorter preform body. However, the closer the center of gravity of the preform to the support ring or the radial projection, the greater the risk that such preforms can wind up in the wrong position. This can also result in problems, for example, even in the case of preforms with a large opening diameter and long outside threadings as well as with a small, light preform body. In many cases, therefore, at the output of the roll sorter, systems can be provided, with which the correct orientation of the preforms can be examined. Misoriented preforms can be removed and fed again to the roll sorter. If the number of erroneously oriented preforms is too large, however, most sorting systems collapse.